Various apparatuses and procedures exist in prior art for acquiring mechanical loads on assemblies. One especially widespread method involves acquiring the expansion of a respective assembly, which can be used for calculating the arising forces, given knowledge of the mechanical properties, such as the modulus of elasticity of the used material.
The expansion is acquired using so-called expansion-measuring strip (“DMS”), which consist of a meandering measuring grid in a thin carrier film, on which the respective assembly is adhesively bonded and then subjected to an electrical resistance measurement. The electrical resistance of the expansion-measuring strip depends on its expansion, i.e., the resistance increases during an expansion, and the resistance decreases during a compression. There is more or less of a dependence on temperature, depending on the design of the expansion-measuring strip. Given a static load on an expansion-measuring strip, a slow change in resistance over time can be noticed, despite a constant assembly expansion. This can be explained by the fact that the expanded measuring grid acts similarly to a loaded spring, which allows shear stresses to come about between the measuring grid and carrier film. These stresses lead to a relaxation of the plastic in the expansion-measuring strip and the adhesive, which preferably arises at the reversal points of the measuring grid. In addition, a certain transverse sensitivity must be observed given a nonlinear load, and both the expansion-measuring strip and used adhesive are sensitive to moisture, so that no constant precision can be achieved during measurement, especially when expansion-measuring strips are used in highly variable environmental conditions.
Mechanical loads are usually not measured in the flap adjustment kinematics of conventional commercial aircraft, in particular in high-lift systems with thrust elements. At the present time, use is made predominantly of overload switches, which protect an actuator that moves the flap adjusting kinematics against overload.
DE 10326799 B3 discloses that mechanical errors in prior art can lead to overloads or undesired behavior on the part of a flap adjustment apparatus, for example an asymmetrical activation of flap elements. For this reason, the entire apparatus may be basically shut down when such errors are detected, and may be locked in their current position by means of braking devices. The disadvantage to this procedure may be the complete loss of functionality associated with the landing flap system in the event of an error.
DE 10004384 C2 shows an arrangement and a method for using an optical sensor to acquire expansions and temperatures as well as changes therein for a cover layer applied to a carrier made in particular of metal, plastic or ceramic. The prior art specified there mentions that expansion is currently determined primarily by means of expansion-measuring strips (“DMS”). In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.